1. Field of the Invention
This invention is concerned with improved processes for recovering copper from copper salts by means of hydrogen reduction in a fluidized bed.
2. The Prior Art
Many processes are of record relating to the recovery of metals by means of fluidized bed hydrogen reduction, including a number dealing specifically with copper. For example, U.S. Pat. No. 1,671,003 to Baghdasarian discloses a process of extracting copper (and other metals) from its sulfide by chlorinating the ore to produce a copper chloride, and reducing the copper chloride to elemental copper by hydrogen reduction. U.S. Pat. Nos. 3,251,684 and 3,552,498 are additional examples of patents which employ hydrogen reduction to reduce copper cations to their elemental state.
A common technique for reducing metals to their elemental state by means of hydrogen reduction is to perform the hydrogen reduction in a fluidized bed. Numerous patents recite various techniques and apparati for conducting fluidized bed operations, including U.S. Pat. Nos. 2,529,366, 2,638,414 and 2,853,361. However, despite these numerous teachings a detrimental phenomenon has been observed in the fluidized bed reduction of cuprous chloride to elemental copper. Within certain processing parameters, the reduced copper tends to sinter and agglomerate, resulting in disruption of the fluidized state of the bed. This phenomenon has not been recognized in the prior art, although Gransden and Sheasby observed a similar phenomenon with respect to the fluidized reduction of iron in their article entitled "The Sticking of Iron Ore During Reduction by Hydrogen in a Fluidized Bed", published in the Canadian Metallurgical Quarterly, Vol. 13, No. 4 (1974). This article discloses that sticking of particles in the fluidized bed reduction of iron ore at temperatures in excess of 600.degree. C. occurs whenever clean iron surfaces impinge. As the temperature of reduction increases, the tendency for iron nucleation also increases. The authors discovered that coating the iron ore particles with a silica film inhibits the iron nucleation and permits iron ore reduction up to temperatures approximating 840.degree. C.
While this solution may be feasible under some circumstances, applicants have discovered a process for preventing sintering of the reduced copper without the necessity of any surface coatings.